1) The cade gun has ten cades that require 450 damage to break. This equates to 4500 hit points to break all ten.
2) The knife breaks the cade in one hit as opposed to 15 right clicks from a regular knife.
3) The knife can only be picked up once, and if the person that has the knife dies, the knife is gone forever, whether they be human or zombie.

My two cents, it doesn't really matter. With the knife it's quicker, but without it just takes a bit longer to get people. And people with the cade guns get stabbed all the time, it's nothing new.